Biological waste treatment is a process which uses microorganisms to consume dissolved organic contaminants in waste water and convert them to additional microorganisms. In aerobic systems, microorganisms are mixed with waste water containing organics and aerated with oxygen for a predetermined amount of time. After aeration, the mixture of microorganisms and water is transferred to a settling zone or clarifier tank where the solid organic contaminants and microorganisms settle, allowing the water at the upper portion of the clarifier tank to be removed while leaving organics in the clarifier.
Aerobic waste treatment for organic carbon removal utilizes biological actions similar to those found in natural waterways. Treatment plants are designed to speed up natural water purification processes and provides means for treating and disposing of waste products from water. "Sludge" and "scum" is made up of mixed culture of bacteria called Zoogloes ramigera. Other microorganisms such as paramecia are also present and are referred to as free swimmers. All these organisms remove organics and some inorganics, by using the materials for food and as essential nutrients.
Microorganisms remove waste water contaminants by absorption and adsorption. Adsorption involves adhering contaminants to the surface of the cells. Material entrapped in this manner is carried by the cell until it is completely digested or disposed of as waste sludge. Absorption involves taking contaminants into the cell. Materials absorbed are completed digested by the microorganisms. In both cases the end products of the process are CO.sub.2 and H.sub.2 O.
Metabolism and energy levels of the biology play an important role in whether or not the cells will coagulate and form large floc particles for good settling characteristics. Performance is based on having enough biological sludge to readily consume the organic pollutants present in the waste water. If biological sludge is in excess, some of it will die and the residue will be discharged in the effluent as part of the TSS. (Total Suspended Solids)
Failure to remove the sludge periodically will result in an anaerobic condition which will sap the oxygen from the effluent and result in a low DO (Dissolved Oxygen) contact and have adverse results in the receiving stream of water. The anaerobic sludge will eventually float to the top of the settling tank where it is referred to as scum and will be carried over into the effluent stream itself. In addition, the contaminated sludge will result in equipment break down in the sewage treatment plant.
If scum is allowed to remain on the clarifier surface, it will dry and form a crust that causes obnoxious odors and may become a harboring place for flies and other insects.
Removal of the floating particles and scum on the surface of the clarifier liquid is usually accomplished by a skimmer which moves the scum into a trough at one end of the tank for removal from the clarifier. Heretofore, skimmers have required large mechanical guiding structure so that the skimmer may be lifted out of the water so that it skims in only a direction toward the scum trough. If the skimmer is moved in both directions in the water, dead areas would form at the ends of the clarifier. The problem with such guide structures is they do not readily adjust for different heights of liquid in the clarifier tank and therefore they remove either too much water, which is undesirable, or not enough scum which makes the system inefficient. Other problems involve the installation of tracks and chains which is expensive and often break down due to the corrosive nature of the liquid in the clarifier.
Heretofore, circular plants have always had the clarifier zone within the center of the tank because the only effective method of skimming the top of the clarifier tank was with a radial skimmer which moved in only one direction in a complete circle. Therefore, it was necessary to build a second clarifier completely outside the perimeter of the circular disposal plant in order to build two complete systems. This meant a dramatic increase in land usage and cost of the plant operation. Heretofore no one has developed an effective skimmer means to skim clarifier zones located on the outside periphery of the circular tank.
My invention is directed toward a skimmer which solves these problems.